1. Field of the Invention
This invention relates to a storage apparatus and a data management method using the storage apparatus, in particular, to a storage apparatus that defines virtual volumes to which storage areas are dynamically allocated, and a data management method for managing the data in the virtual volumes.
2. Description of Related Art
Using disk arrays has been known as a technique to increase the storage capacities and enhance the speed and reliability of a plurality of hard disk drives by grouping them together logically. RAID is a typical embodiment of such disk arrays.
The storage areas in logical volumes provided by the disk arrays are usually consumed with time. Accordingly, a logical volume expanded technique has been proposed, with which, when all the storage areas in one logical volume are used, unused area(s) of arbitrary size in the disk arrays are selected and combined with the logical volume, thereby expanding the storage area in the logical volume.
JP 2003-15915 A discloses a technique with which a volume-providing apparatus that manages a plurality of disk storage devices provides logical volumes to individual host computers. More specifically, when the storage area assigned the logical block address designated in I/O access does not exist in any logical volume, the volume-providing apparatus dynamically allocates an unused storage area in the disk storage devices to the storage areas in the logical volumes so that the logical volume can be expanded.
For the disk arrays, it is necessary to keep track of the operational conditions of the system for smooth operation. JP 2005-196673 A discloses a technique with which the operational information for a storage control system is accumulated in memory and the accumulated operational information is output to a maintenance terminal device.
Because the storage capacity of a storage apparatus depends on the storage capacities of the physical devices such as hard disk drives mounted in the storage apparatus, if a large-capacity storage apparatus is required, that storage apparatus needs to have many devices. Regarding the actual operation of the storage apparatus, it is better, in terms of costs, to expand the storage capacity in a step-by-step manner while monitoring the condition of the consumption of the storage capacity than to prepare a future-required large storage capacity in the first place.
Moreover, in the storage apparatus capable of dynamically allocating storage areas, once a storage area is allocated, mapping information for that allocation has to be created and added to a mapping table. Accordingly, with the increase in the dynamically-allocated storage areas, the mapping table expands in size and consequently increases the load on the search in the mapping information. This may delay the search in mapping information and so degrades the performance in the overall storage apparatus.